1. Field of the Invention
The present invention relates to a miniaturized integrated spectral sensor, with integrated sensed signal conditioning, signal exchange, and integration into a modular sampling system. The sensed information is converted into a meaningful format for process control and is distributed via standard hardwired or wireless communications protocols.
2. Background
Two related aspects of industrial process improvement include the need to understand the process itself, and control of the process based upon that understanding. In particular, it is important to be able to determine the characteristics or parameters at each stage of the process and for the final output of a process, such as the chemical composition, temperature, and/or pressure of reactants used to make a chemical compound, for example. Based upon that information, it is important to be able to adjust the process, such as increasing process temperature, or changing the ratio of reactants, for example, if the output information deviates from an established set of parameters. The inability to monitor the process usually means that there is a risk of low quality product, which results in the need to make corrections, after the product has been made. This is inefficient, and leads to a high level of wastage, which can be compounded by environmental issues.
There are two established approaches to the monitoring of a process for chemical composition or physical properties. They are the extraction of grab samples followed by remote analysis at a suitable control laboratory, and the use of on-line instrumentation. The first option is inefficient and is not effective for control purposes. The second option is usually expensive, and as a result, it is normal to implement a single analyzer at the end of the process. This has limited value for good process control because it is too late in the process to make meaningful adjustments. For a complex process, the ideal situation is to have a multiplicity of measurement points and to monitor the process from the raw material through to the final product. This has to be cost effective to make the implementation of multiple sensing points worthwhile. One solution with optical instrumentation is to use a single analyzer but to multiplex the stream or the optical output. While this is an option, it has risks because it lacks redundancy—one instrument controlling an entire process, and also it is limited in terms of its response, dependent on the number of points being measured (measurements are made sequentially, not in parallel). The present invention uses multiple, miniaturized, low cost spectral sensing devices, a major advancement in measurement opportunity over the status quo, and overcomes issues related to a lack of redundancy. In fact, one may use a redundancy of the sensing devices to ensure maximum efficiency in the event of the failure of a single sensing device. Each device is intended to provide the functionality of a normal analyzer, such as a spectrophotometer, but at reduced cost, and with a significantly reduced size for the total package. While small format sensors exist and are used for standard physical measurements (such as pressure, temperature and flow), these traditional sensors are limited in functionality, and are normally based on changes in electrical properties. The spectral sensing component of the present invention is based on existing optical sensing technology modified for the present purpose. An example component has been marketed as a commercial device by OCLI (a JDS Uniphase company), known as a MicroPac. The device was not produced in a form that was compatible with the proposed application, and was intended only for lab-based experiments that demonstrated feasibility. LVF systems based on a silicon photodiode array can offer spectral ranges of 360 nm to 700 nm (visible) and 600 nm to 1100 nm (short wave near Infrared (NIR)). The original MicroPac device had a complex construction featuring a gradient index (GRIN) lens as an optical interface between the filter and the photodiode assembly. This was required to preserve the spectral resolution of the filter because the detector used was an off-the-shelf commercial detector package. The current implementation uses a simpler construction because it is to be produced as an integrated component as part of the detector array fabrication, by the array manufacturer.
When measuring devices are integrated into a process it is normal to employ a sampling system. The sampling system is typically a collection of valves and sample conditioning devices (filters, mixing chambers, temperature control loops, etc.) that extract the sample from the main stream, and present the sample in an ideal format to the measurement system. Effectively, this is a sample management system, which can include the components to perform reagent-based chemistry for situations where the sensing system requires chemical modification to the sample stream. Traditionally, this collection of valves and components take up a rather large space, and can sometimes be as expensive as the measurement device to implement. In the miniaturization of the sensing devices, it makes little sense to use such a system, in terms of efficiency and cost. Significant benefits are gained if the sensing device and the sampling system can be integrated where the sample volumes are matched to the sensing device itself. Recent developments in industrial process improvement initiatives have been centered on the mechanism for integrating sensing devices into sampling systems. A good example is the New Sensors/Sampling Initiative (NeSSI) sponsored by the Center for Process Analytical Chemistry (CPAC) at the University of Washington, which is an effort by an industrial consortium to standardize sensors and the sensing platform used for process monitoring. Initially, traditional parameters such as temperature, flow and pressure, which can be important indicators of process characteristics, have been addressed. The goal for NeSSI implementation is to make measurement techniques uniform across industries with an interest in participating in the initiative. The platform is a miniaturized, modular version of traditional sample gathering and handling methodologies. Pursuant to the Instrumentation, Systems, and Automation Society (ISAS), standard SP76, establishes the interface of the sample gathering components with sensing devices used to assess the characteristics of the extracted sample. This standard defines both the function and requirements of the sensor system, and provides a specification for the interconnection of the sensor to the modular sensing system. This standard is now supported by all of the major components manufacturers that are suppliers to the industry.
The benefits of the NeSSI system are its size, the ability to add components as standard modules, and the ability to integrate the sensing system to form a single stand-alone unit for sample extraction, conditioning and measurement. The objective is to develop sensing devices that meet the interconnectivity protocols of NeSSI. What is also needed is such a system that enables sampling and sensing at intermediate sites along the way of the process, thereby permitting process corrections earlier and minimizing defective product output. Note that NeSSI has been used here as a discussion point, and is not necessarily the only platform for consideration. There is a movement in a wide variety of fields that involve the handling of liquids, gases and vapors, where miniaturized valves and sample handling/conditioning are involved. This can include miniaturized modular components and manifolds that are fabricated from materials such as plastics, and can include systems that are described as microfluidic sample handling systems. The approach to integration of the spectral sensing devices within these platforms is also important for key applications, such as water chemistry, environmental measurements, and clinical and medical applications.